1. Field of the Invention
The present invention relates to a device for driving a lens adopted in an optical system, and more particularly, to a lens driving device which drives a lens barrel in an optical axis direction more stably to improve optical characteristics of an optical device, generates high drive power with low input power to increase the speed of driving a lens, has a large transport range of the lens, and has a minimal loss of power transmission to increase driving efficiency.
2. Description of the Related Art
In general, optical apparatuses include lens driving devices which move lenses using cam structures, screws or piezoelectric elements. The lens driving devices adopt motors or piezoelectric elements for generating drive power while using cam structures or screws for transmitting the drive power.
Therefore, a lens driving device moves a lens with drive power to change a relative distance of the lens, thereby zooming or focusing.
FIG. 1 illustrates a zoom lens barrel 10 for moving a lens using a cam structure disclosed in U.S. Pat. No. 6,268,970.
In the U.S. Pat. No. 6,268,970, lenses 12a, 14a and 16a are moved along the cam curves formed on barrels 12, 14 and 16, respectively, to maintain relative distances of the lenses necessary for zooming or focusing.
In such a structure, the relative position of each of the lenses 12a, 14a and 16a is determined according to the configuration of a cam structure and an electromagnetic motor is used as a driving source. However, the zoom lens barrel 10 has a plurality of driven reduction gears and is configured to convert the rotation of the barrel moving along the cam curve into linear motion, complicating the structure thereof.
In addition, the above described lens driving device has the plurality of reduction gears, which makes it difficult for miniaturization. Further, it uses an electromagnetic motor, requiring high power, generates electromagnetic waves harmful to humans, and has low positioning resolution of the lens.
FIG. 2 illustrates a zoom lens mechanism of a camera which drives a lens using a screw.
That is, a camera body 22 with an inner space therein has a fixed lens 22a coupled therewith at a subject side. An electromagnetic motor 24 is installed in the inner space of the camera body 22, and a guide screw 24a is coupled with a shaft of the motor 24.
A power transmission member 26 is coupled with an outer circumference of the guide screw 24a, and a lens barrel 28 is coupled with a side of the power transmission member 26.
In addition, a movable lens 28a is coupled with the lens barrel 28, and the barrel 28 is disposed movable along an optical axis with the assistance of a guide shaft 29 that is disposed inside the camera body 22 in the optical axis direction.
Therefore, when the motor 24 operates, the guide screw 24a rotates to move the power transmission member 26 in the optical axis direction. As the power transmission member 26 moves in the optical axis direction, the barrel 28 is guided by the guide shaft 29, moving in the optical axis direction as well, thereby zooming.
However, the zoom lens mechanism 20 of the camera also adopts an electromagnetic motor, thus requiring a plurality of reduction gears, which makes it difficult for miniaturization. In addition, it is impossible to prevent generation of electromagnetic waves by the motor. Further, the mechanism 20 has low positioning resolution, hindering precise control.
To overcome the aforementioned problems, FIGS. 3a and 3b illustrate a driving device 30 for moving a lens using piezoelectric elements disclosed in U.S. Pat. No. 6,215,605.
That is, the piezoelectric elements 32 are fixed to a base block 34 to transmit displacement to driving rods 36, thereby moving the lenses L1, L2, L3 and L4 with preload generated by sliders 38a, together with inertia and acceleration of lens frames 38. According to the waveform of an input voltage, the lens frames 38 move or slide with the driving rods 36 to enable bidirectional driving.
The driving device 30 does not adopt an electromagnetic motor, and thus electromagnetic waves are not generated. It also does not adopt reduction gears for power transmission, thereby simplifying the structure thereof.
However, as the driving rods are essentially fixed, it is impossible to vary the length of the barrel, thus limiting miniaturization. Also, the driving signal has an asymmetrical waveform rather than a stationary sine waveform, complicating a driving circuit.
In addition, when the lenses L1, L2, L3 and L4 are moved, the sliding friction generated between the driving rod 36 and the sliders 38a significantly degrades driving efficiency, resulting in a great loss of drive power. Moreover, the characteristics of the driving rod 36 and the slider 38a may change as they wear out.
Therefore, there arises a need for a lens driving device which can be mounted in a small volume, having a high resolution to enable precise control, and can operate with low drive power while having a sufficient transport range.